1. Technical Field
This application concerns the use of a combination of DNA expression constructs for the production of a remedy for the immunization against infections with leishmaniasis, as well as a corresponding vaccine. The DNA expression constructs themselves are also an object of the embodiments described in the application.
2. Background Information
Leishmania are trypanosmatide flagellates of the order Kinetoplastida. They are passed on to different mammal species and humans by female blood-feeding sandflies of the species Phlebotomus and Lutzomyia. Leishmaniases are diseases with a diverse set of clinical appearances and constitute a major health problem. According to WHO estimates, about 12 million human beings are affected by the disease world-wide. About 2 to 9 percent of all HIV patients suffer from visceral leishmaniasis, making it the third most prevalent parasitic disease afflicting HIV patients. While serious tissue destructions occur with mucocutan and cutan leishmaniasis, an untreated visceral leishmaniasis (Kala-Azar), in most cases, has fatal results.
For the treatment of the disease, there are only a few clinically proved remedies available. Therefore chemotherapeutics—usually compounds of the heavy metal antimony—are used for the treatment of visceral leishmania for about 60 years. The substantially high toxicity of most of these preparations limits their use. Furthermore, leishmania has developed in many regions resistance against antimony preparations (J Postgrad Med. 2003 January-March; 49(1):61-8).
A therapy that is easy to get on and is protective is not yet existent.
Since persons who have survived infection develop a strong immunity against later infections, the development of an effective vaccination should be possible.
The vaccination or, respectively, the immune therapy of leishmaniasis, caused by intracellular parasites, should be possible by inducing a Th1-typical immune response. Within the state of art the importance of inducing a Th1-response in therapy or prevention of leishmaniases is stressed very often (Handman et al., J Immunol 160: 3949-57, Gurunathan et al., Nature Med: 4(12): 1409-15). As support for the induction of a Th1-typical immune response, the co-stimulatory cytokine IL-12 is referred to as being necessary adjuvant (Parker et al., J. Immunol. 140: 896-902).
Additionally, immune stimulatory nucleic acid sequences (ISS) can be used as adjuvant. The CpG-motifs of the ISS lead to an increase of the NK-cell and macrophage activity as well as to a strong stimulation of the cellular Th1 immune response. Covalently closed ISS with a length of 30 bp can preferably be used, as they are described for instance in EP 1 196 178 A1.
Different antigens were tested in various experimental vaccine protocols in mice. The immunological reaction to this infection in mice seems to be similar to that in humans, and probably also to that in dogs (Cox, Int. J. Parasitol. 263: 1147-1157). Antigens employed were gp63 (Scott et al., J. Exp Med. 168: 1675-1684), gp46 (McMahon-Pratt et al., Infection and Immunity 61: 3351-3359), p-4 and p-8 (Scott et al., Immunology 99: 615-624) and the antigen referred to as gp36 or LACK (Gonzales-Aseguinolaza et al., Eur. J. Biochem. 259: 909-916). The most successful vaccination protocol, primary immunization by p36 protein and secondary immunization by vaccinia virus encoding p36 and IL-12, led to an average decrease in lesions of 52% in comparison to non-vaccinated mice (Gonzalo et al., Microbes and Infection: 3 (9): 701-711).
Besides providing the 52% protection, vaccinia viruses have been used in the cited experiments as gene shuttles. Viral vectors represent the most commonly used gene shuttles because of their high transfection efficiency. However, the high risk of a cytotoxic reaction of the host caused by the transfected cells is known. Thus, the application of high doses of an adenovirus led in a clinical trial to the death of the patient; obviously the reason for this was a strong overreaction of the immune system (Lehrman, 1999, Nature 401: 517-518). Furthermore, the metamorphosis of an attenuated vaccination strain into a virulent strain can not be excluded because of its instability. Moreover viral parts themselves can act immunogenically, leading to a decrease of their efficiency by the patient's immune system.
In several experiments of the applicants, BALB/c mice have been immunized with expression constructs coding for the p36 LACK-antigen. Different vaccination protocols have been applied there. Within these studies, in one group a 57% protection against infections with Leishmania major could be obtained (L. Lopez-Fuertes et al., 2002, Vaccine 21: 247-257).
Gurunathan et al. used p36 LACK-antigen, coded by eukaryotic expression vectors, for vaccination experiments in mice (J. Exp. Med., Vol 186, No. 7, (1997): 1137-1147).
In other approaches, different antigen combinations have been used. With a mixture of plasmid DNA, coding for TSA and LmST11, the size of lesions could be minimized over a defined space of time (A. Campos-Neto et al., 2002, Infection and Immunity: 2828-2836). The triple combination of the antigens LACK, LmST11 and TSA could inhibit mostly the appearance of dermal lesions after infection and resulted in protection for several weeks (S. Mendez et al., 2001, J. of Immunology 166: 5122-5128).
All cited experiments have in common that only protection in part—and thus an insufficient protection—against infections with leishmaniasis was possible. Moreover, a big drawback is that the vaccination combinations have not been tested in dogs, the main transmitter, but rather only in mice. A further disadvantage is that plasmids were used as gene shuttles. Plasmids are gained by bacterial fermentation, by which they typically contain, besides the wanted gene DNA necessary for replication and selection, genes that are resistant against the antibiotics used during fermentation. The use of gene expression constructs based on plasmid DNA has the inherent risk of spreading antibiotic resistant genes, which is especially not justifiable at vaccination campaigns. The described disadvantages of plasmid based expression vectors have resulted in massive opposition to their use within clinical practice.